In sheet-processing machines, the individual sheets to be processed are transported intermittently in a cyclic procedure from a feeder which has a device for separating the unprocessed sheets in a stack thereof and for alignedly feeding the sheets to gripper bars of the machine, through various processing stations, such as for example a station for stamping and/or embossing the sheets and a station for breaking off or removing internal waste from the stamped sheets, to a discharge or delivery unit, for example for putting the sheets into a delivery stack. In such an arrangement the processing stations are usually formed from an upper portion and a lower portion, between which the above-mentioned gripper bars pass the sheets. The gripper bars are thus cyclically advanced in an advance plane extending between the upper and lower portions of the respective processing stations, and then, in the same cycle, are returned in the opposite direction to the advance movement, in a return plane which is disposed in displaced relationship in respect of height with respect to the advance plane.
The gripper bars can be fixed to circulating chains and returned to the feeder either above the upper portions of the processing stations, as for example in the arrangement disclosed in DE-OS No 23 24 642, or beneath the lower portions of the processing stations, so that the gripper bars thereby move from the delivery stack back to the feeder.
Such a sheet-processing machine is usually provided with a housing or cowling, for example for safety reasons or for reasons of reducing the amount of noise generated. Provided in the cowling are openings in order to be able to effect set-up and alignment or register operations and in order to be able to observe on-going production. For the setting-up and aligning operations the machine operator must be able to gain access into the machine through the openings in particular in the region of the delivery unit and the waste-breaking-off unit. In that respect most of the operations involved occur above the advance plane of the gripper bars, but to a lesser degree operations are also required below the advance plane. The size of the openings is determined in the advance direction by the spacing of the processing stations or in relation to the delivery unit relative to each other while in the vertical direction the opening size is determined by the spacing between the upper and the lower runs of the above-mentioned gripper bar-carrying chain, relative to the advance plane. The spacing of the processing stations or in relation to the delivery unit with respect to each other corresponds to the spacing of the gripper bars from each other, which is to be kept at a minimum for reasons relating to the dynamics of the machine. The consequence of this is that, in the case of machines for dealing with smaller sheet formats, smaller than about 1 m.times.0.7 m, the openings in the machine cowling become so small that the machine operator can no longer bend therethrough and therefore can no longer implement the necessary operations within the machine. Furthermore, if the gripper bars are returned above the upper portions of the processing station, the upper tool arrangement in the processing stations, for example an upper stamping head, is limited in respect of height as it has to be arranged between the circulating chains. That results in severe limitations in regard to the choice of the operating principle for the stamping head.
The same also applies in regard to the lower tool arrangement such as a stamping head if the gripper bars are returned beneath the lower portions of the processing stations. A further disadvantage in this respect is that the height of the finished stack of sheets is severely limited. It is however an aspect of great importance that stacks of cut sheets constituting blanks for example for making articles should be of relatively great height, for reasons of economy of further processing. If small stacks have to be assembled to constitute higher stacks, further items of equipment are specifically required for that purpose, and that means that the cost, amount of space required and operating time involved are increased. As the chains pass around the delivery stack and the stacks have to be removed in a non-stop mode of operation, that is to say while the machine continues to run, the delivery stacks can only be removed from the machine laterally. The need for space at which the finished stacks are set down, or connections between the sheet-processing machine and subsequent machines, can require the finished stacks to be removed in the direction in which the sheets are advanced through the sheet-processing machine. Furthermore, the fact that the chains circulate below the advance plane of the sheets being processed in the machine means that disposing of waste in the breaking-off unit and in the delivery unit cannot be effected directly, that is to say through openings in the bottom of the arrangement, into a container or a truck.